Genetic and molecular information about dangerous meat allergies linked to tick bites revealed
Key molecules implicated in mammalian meat anaphylaxis have had their structure revealed, paving the way for future treatments
Scientists have revealed the genetic and molecular structure of key molecules linked to the sometimes fatal mammalian meat allergy caused by tick bites.
The study, led by researchers at the Garvan Institute of Medical Research, details how antibodies interact with the sugar molecule galactose-α-1,3-galactose (alpha-gal/α-gal), which is produced by all mammals, except humans. and higher primates. This further confirms the role of α-gal as a key molecule in this unique allergy.
When humans are exposed to α-gal, through bites from certain tick species – such as the paralyzing tick Ixodes holocyclus endemic to eastern Australia – the immune system can flag it as harmful and trigger an allergic reaction, sometimes with almost fatal consequences.
Lead author Professor Daniel Christ, Head of Antibody Therapeutics and Director of the Garvan Center for Targeted Therapy, explains that molecular analysis has shown that a particular type of antibody (3-7) has a pocket natural in which α-gal adapts perfectly.
“We have over 70 types of antibodies and this one is significantly overrepresented with α-gal recognition. We seem to be genetically predisposed to be sensitive to this sugar,” says Professor Christ.
The new study, published today in the journal PNAS, paves the way for potential therapeutic candidates for the treatment of the rare allergic response.
Evolutionary benefit of immune response to α-gal
Scientists analyzed the blood of patients allergic to mammalian meat to determine which antibodies were produced: type 3-7 was frequently found in response to α-gal.
The data indicate an evolutionary advantage of having an antibody response that can mobilize against α-gal.
“Humans lost the ability to produce α-gal during evolution, but we don’t know why,” says Associate Professor Joanne Reed, co-lead author of this study, from the Westmead Institute. “The suspicion is that it has to do with protection against infectious disease.”
Professor Christ mentions recent research on malaria, which shows that the Plasmodium parasite has an α-gal coating on its surface. A rapid immune response to α-gal could destroy the parasite before it takes hold, thus protecting a person from malaria.
NSW is a global hotspot for tick-induced mammalian meat allergy
The Northern Sydney region is a global hotspot for mammalian meat allergy, with over 1800 reported cases and the highest prevalence in the world. Another hotspot is the Sunshine Coast hinterland around Maleny in Queensland. The paralyzing tick (Ixodes holocyclus) is found in these areas.
Professor Sheryl van Nunen, an allergy specialist at Sydney’s Northern Beaches Hospital and co-author of the paper, was the first clinician to link tick bites to mammalian meat allergy. “Not a week goes by that I don’t see two people with this allergy,” she says.
Why some people develop anaphylaxis and others never react is unknown. Professor van Nunen says it could be linked to the number of tick bites, the amount of saliva injected or genetic susceptibility.
Exposure occurs when α-gal, present in the saliva of some species of ticks, is injected during a bite, says Professor van Nunen. About a third of people who have developed sensitivity to α-gal will show symptoms of mammalian meat allergy, she says. And another bite can more than double the allergic reaction. Some people with severe allergies may be affected by the presence of meat products in foods, such as beef broth, soft cheeses such as feta or goat cheese, or gelatin.
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